A spontaneous light emitting display device that configures pixels with light emitting elements such as organic EL elements (OLED: Organic Light Emitting Diode, also referred to as OLED elements) is in a practical stage. An image display device using spontaneous light emitting display elements is characterized by high visibility, not requiring an auxiliary lighting device such as the backlight of a liquid crystal display device, and quick response speed. An organic EL display panel that uses organic EL elements being a paradigm of spontaneous light emitting display elements for current driving changes in light emission luminance, depending on environmental temperatures. The light emission luminance of individual organic EL elements changes also due to secular changes, causing variations in surface brightness of a display area.
FIG. 16 is a circuit diagram showing a first construction example of an organic EL display panel that constitutes a display device equipped with a traditional temperature correction system. FIG. 17 is an explanatory drawing of detection operation points of the transitional organic EL display panel shown in FIG. 16. In FIG. 17, the horizontal axis indicates anode voltages (V) of organic EL element, and the vertical axis indicates a current density (mA/cm2) flowing through an organic EL element. In FIG. 16, the display device includes a display part and a detection unit. In a display area 15 of the display part 100, plural pixels 10 are matrix-arrayed. Each pixel 10 is formed at an intersection of a signal line 11 and a select switch line (scanning line) 12. Moreover, each pixel 10 is provided with an illumination switch line 13 provided in common for pixels connected to the select switch 12, and a power line 14 connected in common for pixels connected to a common signal line 11.
The signal line 11 is connected to a signal line driving circuit 16, and supplies a display signal to a pixel selected by the select switch line 12 and the illumination switch line 13 connected to a display scanning circuit 17. The power line 14 supplies an illumination current to the selected pixel 10 from the power circuit 18 and illuminates the pixel with brightness corresponding to the display signal. A display signal and a timing signal 29 are inputted to the signal line driving circuit 16 and the display scanning circuit 17 from a signal source (not shown) such as a host computer.
The power circuit 18 is provided with a detection unit 200 that includes a detection unit 200 that includes current source 41, a monitor element 20 to detect environmental temperatures, a buffer amplifier 21, an analog/digital converter 22 (AD converter: ADC), and a power control unit 28. The power control unit 28 controls the power circuit 18, according to the output of the ADC 22, based on an environmental temperature detected by the monitor element 20. Here, an organic EL element is used for the monitor element 20.
In the organic EL display panel constructed shown in FIG. 16, a current I1 is fed to the monitor element 20 from the current source 41. At this time, as shown in FIG. 17, the voltage of the anode of the organic EL device being the monitor element 20 is set to a voltage V1 as a high temperature region when an environmental temperature is a defined temperature abnormality, and set to a voltage V1′ in the case of low temperatures lower than it. The voltages V1 and V1′ are inputted to the AD converter 22 through the buffer amplifier 21 for conversion into a digital value. The power control unit 28, when the digital value is small, determines that the system is in the high temperature region, and lowers a power supply voltage of the power circuit. When the digital value is large, it determines that the system is in a low temperature region, and raises a power supply voltage. By using, as the monitor element 20, the same element as that of the pixel 10 provided in the display area, brightness deterioration and variations due to secular changes can be corrected.
FIG. 18 is a circuit diagram showing a second construction example of an organic EL display panel that constitutes a display device equipped with a traditional temperature correction system. FIG. 19 is an explanatory drawing of detection operation of the transitional organic EL display panel shown in FIG. 18. In FIG. 18, only portions different from FIG. 16 are described, and descriptions of common portions are omitted because they overlap. Detection control lines 33 are disposed in parallel with the select switch lines 12 and the illumination switch lines 13. The detection control lines 33 detect current values of pixels connected in common to the select switch lines 12, and output them to the detection scanning circuit 32.
For the detection scanning circuit 32 to detect the respective current values of organic EL elements constituting individual pixels to detect variations in brightness within the display area, and correct them, a detection unit that includes current source 31, buffer amplifier 21, AD converter 22, and signal correction control unit 34 is provided. Changeover switches 43 that include switches SWA (1 to n) turning on and off between the signal driving circuit 16 and the signal lines 11, and switches SWB (1 to n) turning on and off between the signal lines 11 and the current source 31 are provided. The changeover switches 43 operate so that when one switch is on, the other is off, and vice versa.
In a normal display mode, switches SWA (1 to n) of the changeover switches 43 are on, and switches SWB (1 to n) are off. In this state, a signal is supplied from the signal driving circuit 16 to a pixel connected to a select switch line 12 selected by the display scanning circuit 17 through the signal line 11, and the pixel illuminates with brightness corresponding to the value of the display signal by an illumination signal of the illumination switch lines 13 to display a required two-dimensional image.
On the other hand, in a detection mode, switches SWB (1 to n) of the changeover switches 43 are on, and switches SWA (1 to n) are off. Changeover to the detection mode may be made when main power to the image display device is turned on or off, during flyback period, or by a manual operation.
In the detection mode, a current I3 is fed from the current source 31 to organic EL elements of pixels through the signal lines 11 of the pixel side to monitor properties. At this time, a voltage of the anode of the organic EL elements is V3 before deterioration and V3′ after deterioration, as shown in FIG. 19. The voltages V3 and V3′ are inputted to the AD converter (ADC) 22 through the buffer amplifier for change to digital values. When the digital values are below a specific value, the system determines that the organic EL elements do not deteriorate, and does not perform special brightness adjustment. However, when the digital values are greater than the specific value, the system determines that the organic EL elements deteriorate, and the signal correction control unit 34 affords a control signal to the signal driving circuit 16 to correct the display signal.
For individual pixels, their current values are individually detected by scanning of the detection scanning circuit 32 and the signal timing of the signal driving circuit 16, and determined in the signal correction control unit 34. Thereby, even when the organic EL elements deteriorate due to secular changes, high-quality image display free of variations is achieved while maintaining a given brightness.
This system configuration achieves stable brightness control regardless of large variations in environmental temperatures. Such a related art is disclosed in JP-A-2006-048011.